I’ve had similar problems accessing Visual editor after the WP 3.9.1 update and followed semi’s advice to check the them (Weaver II) and all of the plugins. After deactivating and reactivating each one, I was able to isolate the Ultimate Tiny MCE Google Webfonts Addon plugin as the culprit. I have WP Bakery and seems fine. I also am running the Ultimate Tiny MCE and the WP Edit plugins and they seem to work fine (so far). I now have access to all of the Visual editor features I’ve activated.